Ionic-discharge lamp and process of manufacturing same



Dec.- 2s 1926. I 1,612,387

R. R. MACHLETT IONIC DISCHARGE LAMP AND PROCESS OF MANUFACTURING SAME Filed Nov. 25, 1924 2 Sheets-Sheet 1 gwuantoz Dec. 28 1926.

' 1,612,337 R. R. MACHLETT IONIC DISCHARGE LAMP AND PROCESS OF MANUFACTURING SAME Filed I Iov. 25, 1924 2 Sh eets-Shee t 3 W l u:

a. .;.s a%|; Kg I 8: m H l x $5335 31 102144700 N fla ndzzmu zz,

EN I N Patented n. .28, 1926.

UNI-TED STATES P'AraNr orrlca. a

na ruolifncn. macnnn'r'r, or new yonx, N. Y.

rome-msenanon LAMP am) mouse or mmmc'ronme sum.

This invention relates to ionic discharge lamps and processes of manufacturing same; and it relates more particularly to ionic discharge lamps or luminous tubes provided .with externalelectrodes rather than internal electrodes, and filled with a rarefied. gaseous medium, more particularly neon or some other, gas of the noble gas group which inpasses bearing a predetermined relation to the impedance of the electrode system; and the invention further relates to the process of manufacturing tubes of this character in sue h manner as to secure long life and contion is that the effective impedance of the glass electrode system when the tube-is inoperation 1S less, and most desirably very much less, than the impedance ofthe gas stancy in the light produced by such tubes.

When ionic discharge tubes having internal'electrodes are run continuously, the pressure within them tends to change and in general to becomeless. This is dueprincia pally to chemical and physical absorption of the gaseous medium by the metallic electrodes used in such tubes. Such absorption is caused by phenomena generally known as sputtering, through the action of which metal from the electrodes is gradually deposited on the walls of the tube nearthe respective electrodes, such metal forming a thin coating on theglass which occludes the gaseous medium, sometimes to a considerable extent. Thus, the pressure 1s. dimmished until finally the discharge becomes feeble or steps entirely. In order to over- I .tion, or success.

come this,'large' cumbersome metallic electrodes aresometime's used, but even in this case s uttering [is not entirely eliminated. It is a so difiicult to degasify and clean metal of the electrodes of theusual ionic discharge tube, a veryessential point in manufacturing such tubes. It is also found that unless such electrodes are fully degasified and cleaned, the light in the tube is likely to change in color due to its contamination from volatile substances occluded insuch' metal electrodes.

It has been proposedheretofore to employ external electrodes with gas filled tubes, but sofar as this applicant is'aware-such roposals have'resulted in'no practical app icapresent invention, use is made of external electrodes as contrasted -with-interna1 electrodes, and the employment of such external electrodes is rendered of practical value In accordance with the Application filed November 25, 1924. 8erla1 No.752,288.

through certain precautions taken in the coursb of manufacturing the tubes, and in the observance of proper electrical conditions WhlCll this applicant has found to be essential to success. Ingeneral the manufacture of a lamp or luminous tube in accordange with the principles of this invention lnvolves a very thorough elimination from the glass of the tube of impurities that could later be evolved therefrom and render the contained gas im 'ure. In furtherance ofthls ob ect the finis ed tube as 'ordinarily constructed contains a small amount of a suitable gettering material, which functions during the life of the tube to preserve the purity of the: contained gas. Another important feature of a tube constructed in accordance with the principles of the invencontained in the tube.

The principles of the invention will be more fully understood in connection with the following description of a practical embodiment of a tube involving the underlying principles involved and of a practical proc ess of manufacturing the same, particular reference being made to the accompanying drawings, in which- Fig. 1 illustrates a practical form of the novel luminous tube, together with a typical operating circuit system shown more or lessi ings, the luminous tube here illustrated consists of a neon-filled tube having terminal portions A which in this instance have an external coating'a of silver or other easily deposited metal constituting the external electrodes. In the form of tube here illustrated, the terminal or electrode portions of the tube are shown as larger than the intermediate portion, but this is not essential to the invention in its broader aspects and. is

governed to a large extent b the particular frequency of the current to used in operating the tube, the important'point being that a proper relationbetween the impedance of the glass electrode system and the imdistribution of Qpedance in the system-as the present specification an a whole should be suehethattheener loss occurs chiefly in the gas in the tube an relatively little in the glass electrode system. In achieving this result, it has L found that frequencies of the order of 7 50,- cycles second can be used with good results,,but t is figure is mentioned merely by way of example and is not intended tq be restrictive.

The use of frequencies of this order of magnitude permits the use of relatively small external electrodes, and for; this reason such frequencies are especiallv desirable. However, the use of the term hi h frcquency'1n C claims is to be understood as not restricted to frequencies of such large magnitude, but rather to'include frequencies down to 10000 or as much lower as will not require provisiorfof excessively large electrodes in order to maintain impedance distribution as abovedescri Fig. 2 illustrates another form of external electrode A" having double glass Walls 10 and 11, the space between these walls being filled with finelydivided graphite or other conductive material 12 in powdered form.

B means of electrode constructions such as tliose here shown as A and A, and when the tube is filled with neon, for example, to the proper pressure, usually about 4; -milli-. meters mercury absolute, for example, a glass condenser electrode is formed. It is seldom necessary for the pressure to be outside the range of 3 to 8 millimeters. The high frequency current employed to operate the tube-is of such character, having in mind the impedance relation hereinbefore mentioned, that this arrangement will easily pass considerable current, commonly from 5 to 20 milliamperes in a typical design of tube,

with a resultant glow withinthe tube.

This glow varies in intensity and color depending upon. the character and urity of i the is: and the current density. *1 the tube has n carefully exhausted, baked at high temperature during exhaustion, and other wise properly prepared, the light in the tube will be bright and characteristically the color of the excited gaseous medium with which the tube is filled. In the case of neon, at the proper pressure, this glow is a brilliant orange red.

In the typical operating circuitarrangement shown in'Fig. 1, leads 13' and 14 connect the external electrodes A of the tube with the secondaries 15 and 16 of Tesla coils of which the primaries are indicated at 17 and 18, these primaries being opp ositely wound, These primaries 17 and 18'are 1ncluded in an oscillating circuit, actuated by a current breaker mechanism indicated generally at 19. This oscillating circuit consists of the breaker mechanism,condenser 20 and primaries 17 and 18 of the-Tesla coils which are connected' in 'series as shown and constitutea suitable oscillating circuit for the operation of-the tube. Other arrangements acrggiplishing this same general result canbe but that here shown is simple and convenient.

The primary oscillatin circuit should be 'of such design that its resistance to high he i queney currentsand its free distributed capacity are kept at a minimum. This is for the reason that these lamps are often used for electrical display sign purposes. when they are bent into the ,outline forms of letters or into designs. Thus thepart's of the tube may be so shaped and placed with relation to other parts of the tube and to grounded'materials in the vicinity of the tube to have considerable tendency to shunt,

off the energy from its true course b the capacity s0 established. This ten ency is nown to increase as the tube is subjected to continued operation because the voltage drop across'the tube becomes greater due to slight decrease in the gas content. Thus if the electrical mechanism isnot designed to eliminate as far as is possible the high frequency resistance and distributed capacity in the 3 Ezimary oscillating circuit, the energy will expended within the mechanism and not in the gas of the tube. It istherefore advisable to keep all wires of the rimary oscil lating circuit short, heavy and well spaced; and it is furthermore advisable to employ Litz wire (Litzendraht) in winding the primaries of the Tesla coils. By this means the capacity and resistance of this circuit are kept so low as to be negligible as compared to terminals 21. i a

The 0 eration of this type of glass consv denser e 'ectrode is accompanied, unless the current passed through the tube is extremely small, by slow decomposition of the glass itself, es ially at the glass electrode ends. The pro nets of decomposition are mainl to .the ca acity of the tube in its circuit. The oscil atlng circuit may be energized -from commercial DC or AC mains connected water va r, but thereare also'other pro ucts; an all are detrimental'to the perfect operation of the tube. The additiom of such impurities to the gas cause", it tolose is brilliancy'and'color, as well as much of its conductivity. Accordingly, in the manufacture of the tube itis desirable to introduced into one 'or both ends of the tube, as at C, some material having the property of absorbing chemically or physically such impurities as they appear in the gas content of the tube 1 during its life. The introduction of such a material into the tube of the invention is therefore a desirable feature of the process of its manufacture, and the material is of course left within the tube permanently. Such material is found advantageous also because it. facilitates production of a uniform product in actual manufacture with less difficulty in the matter of'cxhausting the tube. As examples of uitable absorbing agents may be mentioned an alkali metal such as potassium or sodiumfior activated charcoal. The alkali metals havethe prop erty of absorbing oxygen or other undesirv able gases which are either initially present or which may be developed within the tube in operation. -Activated charcoal functions similarly by rea on of it physical characteristics. The absorptive or gettering agent employed may be lo ated at any po nt in the tube, but it is generally preferable to place it at one or both ends of the tube.

In iiianlif ictiii'ing the novel dischargd tube, employment of the apparatus system illustrated in Fig. 3 has been found to give especially good results. At 22 is an oven heated by ga or other suitable medium within which is suitably supported the discharge tube indicated generally at 23. Sealed to one end of the tube is a series of glass containers 24,25, 20 and 27, the function of which will appear presently. The other end of the tube has sealed to it a glare-3 tube 28 by which it is connected to an exhausting system of any type suitable to produeevery high vacua. In this instance, the vacuum producing system comprisesa 1nercury diffusion or aspirator pump 29 capable of pumping at such a rate that the dega ifi cationof the glass is readily accomplished. This pump is supplied with the usual freez ing traps 30. 31, and with a suitable fore pump 32. The system is also supplied with a gage 33 for measuring the .prei sure in the lamp. The system for introducing the-puritied gas into the lamp comprises the gas container 34 and magnesium are 35 which constitutes a convenient means for purifying the gas, such as neon, that is to be supplied to the tube. It is to be under tood, of course, that other suitable purifying. means can be used in place of this specific means.

The tube is first baked at about 420 C. or thereabouts until gas ceases to be evolved from the glass. Means for'determinin this fact positively is indicated at 36 wh ch is an ordinary spectrum tube provided with means 37 for applying high potential at its terminal electrodes. The test consists of closing the glass cock 38 and applying the potential to the spectrum tube 36, while continuing the operation of the diffusion or aspirator pump 29 which of course has been inoperationfrom the beginning. The withdrawal the tube 23 by the diffusion pump gives a very pronounced indication in thespectrum tube 30, so that this is a very delicate test.

WVhen after some lapse of time, say three to five minutes, light ceasesto appear in the spectrum tube 36, the fact that gas ,has ceased to be evolved in the lamp is established. Up to this point th process has u ually consumed; from twenty to thirty minutes.

The oven 22 is so adjusted thatcit. takes a definite time, say fifteen minutes for example, to reach a temperature of 300 C. in heating up. During this interval, that is, up to the time that the temperature reaches 300 (1.. the tube is continually excited with a high frequency current, preferably soyapplied as to cause a greater current to pass through the tube than will be expected of it in final operation. Means for thus exciting the tube during the operation of heating up is indicated generally at 39 which may be any suitable generator of high frequency currentof high voltage connected as shown to the; terminals of the tube. Due to the heating of the. tube. there is sufiicient gas being constantly evolved to provide the necessary conductive path for passage of the currentthrough the tube. The passage of high frequency current through the tube at this stage greatly expedites final exhaustion.

Excitation of the tub while, at a temperature between 200 and 300 C. is especially desirable because, over this range, gases evolved'in the tube. including those dislodged by the ionic discharge, are prevented from re-settling on the glass walls.

After the baking of the tube is complete, as determined by the spectrum tube testabove referred to. a suitable ab orptive agent of the character already mentionedis introduced into the tube. Potassium is especially desirable for this purpose and is employed in the present illustrative example. The. necessary quantity. of potassium having been placed in the tube 24 at the beginning of the process, it is now distilled successively into the containers 25. 26 and 27, which are also successively sealed off. and then finally into the end of the discharge tube, this succession of distillations beingfor the purpose of eliminating'minute quantities of impurities. During the introduction of the potassium into the discharge tube, the tube should be ma ntained fairly warm. that is, at a temperature that will permit the potassium to condense into the discharge tube but which will not permit any more volatile impurities which may be contained in the potassium and which are not retained in the bulbs 25, 26 and 27 from remaining in the discharge tube. In this connection, it is of course to be understood that during the enti e process the difiusion or aspirator pump 29 is kept in continuous operatlon.

The difiusion' pump is now cut off and-the lamp is filled with neon lat low pressureyop eratcd for a few minutes by the source'of ex citation and again exhausted by the pump. The final charge of. neon is then admitted, the pressureadjusted to the proper value, and the tube is sealed o'fi.

This lamp operates-with the greatest degree'of rfection only when it is supplied with high-frequency current as hereinbefore stated, the actual freque ncyof such current being such'that the effective impedance of -.the glass electrode system is less than the impedance of the gas betweenthe electrodes. Withinreasonablelimits, the adjustment of this impedance ratio can be effected by varying thejconductive areas of the electrodes, but this method is much more limited in practical application than is the method of adjusting the frequency. Upon this balance of value depends the long life and pure color ofthe lamp without internalclectrodes.' If this balance of values is destroyed and, for

example, the frequency of the exciting current is so low that the efi'ective impedance of the glass condenser electrodes is greater than the impedance of the gaseous medium 30 between the electrodes, the operation of the lamp is accompanied byheating of the glass immediately associated with the conductive coating forming the electrode, with consequent evolution of impurities from such glass, which impurities destroy the desirable high conductivity and also afiect adversely the color and brilliancy of the light afforded by the tube. I i

-While-specific embodiments of the new tnbe' and its process of manufacture have been hereinabove described for the purposes I of a detailed explanation of the principles ed claims.

underlying the invention, it is to be understood that the invention is not restricted to such details but is susceptible of considerable' variation within the scope of the append- What is claimed is: '1-

. Leia-gas: Q

1. c The. combinatiom'f with a gas-filled luminous discharge glass tube having only ex- 60 ternal electrodes; of means for impressin upon said electrodes alternating. potent-ia sufiiciently high to"; produce operative current flow through thetube, said potential bein}; of such frequency that the effective impedance of the glass electrode system is less than the impedance of the gas in said tube. 2. The combination, with a gas-filled luminous discharge glass tube havin terminal portions each provided with a conductive coating constituting-an electrode separatedby thejwall of. the tube fromthe gas contained in said tube, of-means for impressing upon said coatings alternating potential of operative magnitude, thefrequency of said 55 supply high frequency current of operative potential thereto, said circuit means including a primary oscillating circuit in which I the resistance to high frequency and free distributed capacity are low.

.4. The combination, with an ionic discharge lamp, neon-filled to a pressure of from 3 to 8 millimeters of mercury absolute 'andcontainin a small quantity of gettering material, sai lamp being provided with glass condenser electrodes, of means con- 35 nected to said glass condenser electrodes for impressing thereupon alternating potential of operable magnitude and of such frequency 'thatfthe (affective impedance o'fthe glass electrotie system is less than the lmpedance of the gas in said tube. I

In testimony whereof hereunto aifix my signature.'

' RAYMOND R. MAOHLETT. 

